In general, as an X-ray tube assembly, a rotating anode X-ray tube assembly is used. The rotating anode X-ray tube assembly comprises a rotating anode X-ray tube configured to radiate an X-ray beam, a stator coil, and a housing accommodating the rotating anode X-ray tube and the stator coil. The rotating anode X-ray tube comprises an anode target, a cathode and a vacuum envelope, and uses a dynamic pressure type sliding bearing.
The sliding bearing includes a cylindrical rotor, a fixed shaft engaged with an internal part of the rotor and supporting the rotor in such a way as to allow the rotor to be rotated, and liquid metal filled in a space between the rotor and the fixed shaft. For example, the fixed shaft includes a first bearing surface and a second bearing surface which have respective spiral grooves formed therein. The rotor includes a third bearing surface. The first to third bearing surfaces are radial sliding bearing surfaces. The first bearing surface, the third bearing surface and the liquid metal form a first bearing (radial sliding bearing). The second bearing surface, the third bearing surface and the liquid metal form a second bearing (radial sliding bearing).
In an operating state of the rotating anode X-ray tube assembly, the stator coil generates a magnetic field to be applied to the rotor, and thus the rotor and the anode target are rotated. Furthermore, the cathode radiates an electron beam to the anode target. Therefore, the anode target radiates an X-ray beam when colliding against electrons. Of kinetic energy of electrons colliding against the anode target, slight kinetic energy is converted into an X-ray beam, and most kinetic energy is converted into heat.
The anode target is connected to the rotor, with a supporting member interposed between them. This structure can reduce the amount of heat to be transmitted from the anode target to the rotor, as compared with the case where no supporting member is used.